Aqueous suspensions comprising hydraulic binders that are commonly called “slurry” come in the form of more or less fluid suspensions. The advantage of such suspensions is that they form ready to use solutions to be directly employed in any application for construction chemistry such as adhesive formulation, soil preparation, floor covering, tile flooring, wall preparation, exterior rendering, concrete repairs, ready-mixed concretes, shotcretes, sewerage systems, waterproofing, road repair works, binding, anchorage devices, paints and coatings and prefabrication and refractory and peri-refractory applications.
Stabilization consists in stopping hydration of the hydraulic binder by adding a blocking agent (or inhibitor). Amongst known blocking agents, boric acid and salts thereof reveal particularly efficient for stabilizing hydraulic binder-based aqueous suspensions comprising aluminous cement.
The patents EP 0241 230, EP 0 113 593, the patent application EP 0081385 and the French certificate of utility FR 2763937 disclose, for example, compositions comprising an aluminous cement in aqueous phase which has been retarded for several months through addition of boric acid, or a salt thereof, being suspended in water.
However, using such a blocking agent has some drawbacks. The aluminous cement aqueous suspensions are not stable for sufficient periods of time at high temperature. This phenomenon is even more marked when these aqueous suspensions are associated with resins or organic binders. This phenomenon gets worse when the aqueous suspension is used in high proportions as compared to the aqueous suspension—organic binder mixture.
Another drawback of boric acid is that it is quite toxic and ecotoxic as well.
US 2004/211562 and US 2004/211564 disclose cement composition comprising by weight/weightnon hydrated cement: 20 to 80% of calcium aluminate; 20 to 80% of a silica source (fly ash); 1 to 10% of a soluble phosphate like sodium polyphosphate, sodium hexamethaphosphate, sodium phosphate or a mixture thereof; 0.1 to 5% of a set retarder (carboxylic acid like citric acid; tartaric acid); and 30 to 50% of water to obtain pumpable slurry. The function of the soluble phosphate is to improve the corrosion resistance of the cement composition. The examples in US 2004/211562 show that the set retarders tested retard the hydration of the cement compositions up to a maximum of 16 hours.
Thus, the use of a carboxylic acid as blocking agent does not provide aqueous suspensions of aluminous cement which are stable for a sufficient period of time, such as for example, one month.
JP 2007/254196 discloses a hydraulic composition comprising: aluminous cement, Portland cement, gypsum (the total of the three components is 100 parts by weight), water and optionally, a set modifier. The set modifier is sodium pyrophosphate (Na4P2O7) and/or sodium tartrate.
KR 100 913 496 discloses a dry concrete composition for paving to improve drainage and water retention. The composition comprises a binder and aggregates having a mean diameter between 2.5 and 5 mm. In particular, the binder is a dry composition based on a calcium sulfoaluminate clinker, gypsum, an intensity accelerator selected for example from alkaline metal carbonates or bicarbonates and a retarder.
US 2008/302276 discloses a cement composition in the form of a rapid set aqueous composition comprising: active hydraulic cement (Portland cement, calcium aluminate, calcium sulfate and fly ashes), set accelerators, water and optionally, set retarders selected from citric acid, sodium citrate, sodium tartrate or potassium tartrate. The set accelerators are selected from a mixture of an alkanolamine and a phosphate or polyphosphate (sodium trimetaphosphate, sodium or potassium tripolyphosphate, tetrapotassium or tatrasodium pyrophosphate) that act in synergy. The rapid set of the aqueous composition occurs by mixing the different components at a temperature above 32.2° C.
Therefore, it is necessary to find new blocking agents for aqueous suspensions comprising aluminous cement and/or calcium sulfoaluminous cement which would not suffer from the hereinabove mentioned drawbacks.